The present invention relates to control means and methods for food processing devices useful for cooking, storing or modifying food at selected conditions of temperature and humidity until the food is to be served. Devices within the scope of the present invention have been found useful where food is to be processed, cooked, proofed (as described hereinafter) or held under controlled conditions or and combination thereof.
With the increasing popularity of "fast food" establishments where food is precooked for later sale, there is a demand for food holding devices to maintain food at substantially uniform temperature for selected periods of time while preserving the taste, moisture content, texture and quality of the food. Further in other applications it is desirable to be able to restore food, particularly baked goods, to acceptable quality after long storage periods.
In many instances storage of "fast foods" is particularly difficult because heat loss, bacteria growth and moisture loss experience by the food at storage conditions provided by prior art devices, particularly where the food is to be stored warm, contribute to rapid deterioration of the food.
More particularly, it has been found that air circulation characteristics and improper storage temperature contribute significantly to bacteria growth and excessive loss of moisture which leads to food shrinkage, so that in improper storage atmosphere the food deteriorates after only a short period of time and loses its tenderness, appetizing taste and appearance.
In accordance with another feature of the present invention it has been found that even where food is stored under favorable conditions in an enclosure, the food deteriorates at a rate dependent on the time the door to the enclosure is opened so the storage chamber is exposed to the ambient atmosphere.
Additionally, it is known that in storage of some foods such as fried chicken or fish where a crust is provided, it is particularly desirable to maintain the crispness of the crust while minimizing the moisture loss from the underlying meat. Storage of such foods tends to require the satisfaction of seemingly mutually exclusive conditions, to hold the crispness of the crust by maintaining low moisture content in the crust while minimizing moisture loss from the food. In such foods excessive moisture loss results in shrinkage and loss of tenderness and adversely affects the texture of the meat. This can be prevented by controlling the temperature and humidity of the storage atmosphere. The problem is to prevent moisture flow from the underlying food to the crust while holding the crust in low moisture content.
The prior art demonstrates various means for storing food such as shown in U.S. Pat. No. 4,038,968, U.S. Pat. No. 3,955,077, but neither provides for selective humidification and temperature control of warm moist air passed around a food by regulating the application of energy to a heater in a water reservoir or to an air heater to maintain the food at a uniform temperature while attempting to maintain moisture in the food.
Additionally, U.S. Pat. No. 3,955,007 utilizes a moisture container assembly mounted in a heat holding compartment located above a gas burner assembly where the amount of moisture added to the circulating air bears no relationship to the temperature of the air so the moisture content is subject to change with the rate of the heat supplied to the humidifier.
One arrangement for maintaining the moisture content and temperature of food products and for slowly cooking foods in some applications is shown in copending U.S. Application Ser. No. 521,344 filed Aug. 8, 1983.
It is further recognized that prior art devices which provide only saturated air to a storage compartment do not recognize the dynamics of food storage and can lead to situations where breading crust, or other materials on the surface of a food product become soggy so the food looses its appeal even though the underlying meat may not loose its moisture. Or in some instances the food product loses its moisture to the crust so the worst possible situation arises. Such problems are further compounded when the food is frequently exposed to the atmosphere as by the door to the storage compartment.
One known prior art reference U.S. Pat. No. 2,318,027 Sykes teaches a dehydration device where temperature and humidity are controlled in an enclosure by sensing wet bulb and dry bulb temperatures and spraying steam into a water reservoir to increase humidity. The use of heaters to maintain selected water reservoir temperature is not taught.
Another prior art reference, U.S. Pat. No. 3,245,461 Allington, teaches a control arrangement to maintain humidity by monitoring wet bulb and dry bulb temperatures where cooling or heat is supplied to a water reservoir in response to change in wet bulb and dry bulb temperature. Nowhere does the reference recognize the value of the use of the reservoir temperature as a means of controlling the treatment of food.
U.S. Pat. No. 3,518,949 Stock teaches an arrangement for conditioning dough etc. where a first control is provided to control air temperature in an enclosure by operation of a heater, second temperature control means are provided to limit the maximum temperature adjacent the heater and a humidity responsive switch is provided to energize a heater in a water reservoir to vaporize water to adjust humidity. Stock, like Allington and Sykes, does not teach control of the water temperature. Additionally, Luce U.S. Pat. No. 2,939,423 controls humidity by controlling temperature of the air and water but does not independently control air and water temperature. U.S. Pat. No. 3,424,231 Truhan, teaches controlling air and water temperatures but sprays water into the air, saturating the air at the water temperature rather than relying upon the exposed surface of the water in the reservoir to emit vapor into the air.
No prior art device is known which recognizes the advantages of simultaneous control of humidity and temperature of the air in a food storage compartment to maintain control of the quality of the food and even permit cooking of the food by periodic alternate and/or cycled variations in the application of energy to heating devices which control the temperature and vapor pressure of the atmosphere to which the food is exposed.